Instrument for making electrical measurements.



No. 804,190. PATENTED ov. 7,1905 I J. A. FLEMING. INSTRUMENT FOR MAKINGELEGTRIOAL MBAsuREMN Is.

APPLIOATION FILED FEB. 8. 1905.

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UNITE STATES PATENT FIQE.

JOHN AMBROSEFLEMING, OF LONDON, ENGLAND, ASSIGNOR TO MARCONIS WIRELESSTELEGRAPH COMPANY, LIMITED, OF

LONDON, ENGLAND.

INSTRUMENT FOR MAKING ELECTRICAL MEASUREMENTS.

Specification of Letters Patent.

Patented Nov. '7, 1905.

Application filed February 8, 1905. Serial No. 244,714.

To all whom it may concern.-

Be it known that I, JOHN AMBRosn FLEM- ING, professor of electricalengineering, a subject of the King of Great Britain, residing atUniversity College, Gower street, London, in the county of Middlesex,England, have invented certain new and useful Improvements inInstruments for Making Electrical Measurements, of which the followingis a specification. Y

This invention relates to improvements in instruments called cymometers,for the measurement of wave lengths and frequencies employed inHertzian-wave wireless telegraphy, and for other electrical measurementssuch as small capacities and ind uctances. In space telegraphy of theabove kind, the distance to which it is possible to propagate signalsover land or sea depends very much upon the length of the electric waveused and it is necessary to be able to measure this wave length withoutdisturbing the apparatus employed for sending. I do this by constructinga closed oscillating circuit consisting of a capacity in the form of acylindrical sliding condenser and a helical variable inductanceconnected together so that one motion reduces or increases both theinductance and the capacity at the same time. Since the frequency in anoscillating circuit varies inversely as the square root of the productof capacity and inductance, this has the effect that the totalalteration of the arrangement varies as the wave length. The condenseris formed of two concentric metal tubes. The dielectric of thiscondenser must be ebonite or some material which does not vary with thefrequency and is a very good insulator.

Figure 1 is a side elevation and Fig. 2 an end elevation (some partsbeing omitted) of an instrument constructed according to this invention.Figs. 3 and 4: are similar views of a modification.

e e is an ebonite tube which has within it and partially projecting fromit a brass tube I. This brass tube has connected to it another ebonitetube S S on which is wound a spiral of thick copper wire which mayconveniently be the size called No. 14, standard wire-gage. The ebonitetube on which this spiral wire is wound is smaller in diameter than theebonite tube 6 e. and fits within it. The spiral of copper wire shouldbe wound in rather open turns,

the turns being about one-eighth inch to onefourth inch apart and theouter end of the wire is attached to a metal pin p fixed in one end ofthe smaller ebonite cylinder, while the opposite end of the wire isinsulated. On the ebonite tube 6 3 slides an outer brass tube J whichcarries a bar a a terminating in a collar K, the said collar having aninsulating-handle of ebonite H. This outer jacket must be of such adiameter that it can slide easily upon the ebonite tube 6 6, while atthe same time, the collar K makes good electrical contact with spiralwire S S, the jacket and collar being moved by the handle H. The innerbrass tube I has connected to it another pin 39 and the two pins 19 79are connected by a stout copper bar L L L L It will be seen that thearrangement constitutes a condenser in series with an inductance andthat when the handle H is moved along the spiral this action at the sametime reduces the inductance of the circuit and the capacity formed bythe two metal cylinders I and J separated by the dielectric 0. Withregard to dimensions I have found it convenient in constructing aninstrument to measure wave lengths up to two thousand feet, to adopt thefollowing dimensions: The ebonite tubec 6 may conveniently be fourinches in diameter, the thickness of the sides should not be less thanonetenth of an inch and the length of the tube about three feet. Theouter brass jacket may be twenty-eight or thirty inches in length andthe ebonite tube S S should also project for the same length beyond theebonite tube 0. The jacket 1' is conveniently made by bending round theoutside ebonite tube a thin sheet of brass which is clamped by screws 6/a to a rectangular bar a a so that just the requisite degree oftightness may be given to this jacket enabling it to move smoothly andyet fit closely on the ebonite cylinder. The inner metal tube 1 shouldlit the inside of the ebonite tube a closely and project beyond it forthe distance of an inch or so. The rod L L L L may consist of a strip ofcopper about an inch in width and about one-eighth of an inch inthickness.

In another form, shown in Figs. 3 and 4, I make the outer jacket J fixedand the inner jacketmovable. The arrangement then consists of an ebonitetube 6 which may conveniently be about four feet or four feet six inchesin length and four inches in diameter outside. This tube is embraced onits outside for about half its length with a metal jacket J formed ofthin sheet metal bent round the tube and clamped together by screws aa,the other half of the ebonite tube is wound with a bare copper wireput on in an open spiral, the turns being about one-eighth to one-fourthinch apart and in all cases it is best to out upon the ebonite tube agroove in which this wire partially lies. In this arrangement one end ofthe copper wire is connected to the jacket J and the other to a metalcollar cl having an insulating-handle H. Inside this ebonite tube 6 isanother brass tube I, which fits closely but it can slide in and out ofthe ebonite tube. The circuit is completed by a copper strip L L L L asabove described, but in this case the copper strip ends in the collar K.One end of the brass cylinder I has a pin 19 attached to it and this ispivoted to one end of the copper strip. By taking hold of the handle Hand moving the ebonite cylinder along, the ebonite tube a is drawn moreor less off the inner metal tube I and at the same time the eflectiveportion of the inductancecoil S S included in the circuit is shortened.In this manner the capacity and the inductance of the circuit arereduced together. The instrument is provided with a vacuumtube Vof thetype employed in spectrum analysis consisting of two bulbs united by anarrow glass tube and this vacuum-tube is preferably constructed ofuranium glass and filled with rarefied carbonic-acid gas, 0r,,betterstill, the rare gas called neon. This vacuum-tube is attached to theouter jacket J and moves with it. On the straight portion of the copperstrip L L is engraved a scale 0 and one end of the vacuum-tube shouldnearly touch this scale.

The instrument is used in the following manner: A determination mustfirst be made of the electrical capacity formed by the two cylinders 1and J separated by the ebonite tube when the cylinders are moved intodifferent positions, and also of the inductance of of that part of thespiral included in the circuit corresponding to the same position of thecylinders. These measurements are made by well-known laboratory methods.Let C denote the capacity of the cylinders in any V sition.

10. In any oscillatory electric circuit containing capacity andinductance, the frequency of the oscillations in that circuit isobtained by dividing the numberfive millions by theoscillation constantof the circuit, as above described. Again if oscillations are set up inan open electric circuit, such as an aerial Wire, electric waves areradiated from this wire and these waves haveacertain wavelength. Thevelocity with which these waves travel away from the wire is very nearlyone thousand million feet per second, and the relation between the wavelength of the waves and the frequency of the oscillations in the wire,is given by the following rule. The wave length in feet multiplied bythe frequency is equal to one thousand millions. I-Ience if we candetermine the frequency of the oscillations in a vertical wire, such asan aerial Wire used in wireless telegraphy, by any means, the wavelength of the waves can be determined. Also since the frequency of theoscillations in any circuit is connected with the oscillation constantof that circuit. as above described we have the following simple ruleconnecting together the oscillation constant in an open electric circuitradiating electric waves and the wave length of the waves radiated, viz:YVave length in feet equals two hundred multiplied by oscillationconstant. Either of the above forms of cymometer enables thisoscillation constant to be measured at once. Thus supposing there is anaerial wire which forms the radiator of a wireless-telegraph transmitterand it is desired to find .the wave length of the wave radiated, a partof this aerial wire is laid parallel to the copper bar L L of thecymometer and when the wireless-telegraph transmitter is in operationthe handle H of the cymometer is moved to and fro until such a positionis found that the vacuum-tube V glows most brightly. When this is thecase, the oscillation constant of the cymometer agrees with that of theaerial radiator and the numerical value can be read off upon the scaleof the cymometer, provided that the oscillation constant lies within therange of the cymometer used. In th-ismanner by one single operation Imeasure at once the frequency of the oscillations and the Wave length ofthe Wave sent out from the transmitter.

What I claim is- .1. The combination ofa condenser, a coil in serieswith the condenser and means for simultaneously varying the capacity ofthe condenser and the inductance of the coil, in the same proportion.

2. The combination of two conducting-surfaces, adielectric between thesurfaces, acoil having one end connected to one of the surfaces, acontactmaker resting on the coil and connected to the other surface andmeans for simultaneously moving the two surfaces and the coil andcontact-maker relatively to each other respectively.

3. The combination of two conducting-surfaces, a dielectric between thesurfaces, a coil having one end connected to one of the surfaces, acontact-maker resting on the coil and connected to the other surface,means for simultaneously moving the two surfaces and the coil andcontact-maker relatively to each other respectively, and avacuum-tubecarried by one of the surfaces.

4. The combination of two concentric metallic cylinders, anon-conducting cylinder fixed to and projecting beyond one of them suchcylinder being adapted to fit between the two metallic cylinders, a coilwound on the projecting portion of the non-conducting cylinder andhaving one end connected to one of the metallic cylinders and acontact-maker resting on the coil and so connected to the other metalliccylinder that it always occupies the same position relatively to it.

5. The combination of two concentric metallic cylinders, anon-conducting cylinder fixed to and projecting beyond one of them suchcylinder being adapted to fit between the two metallic cylinders, a coilwound on the projecting portion of the non-conducting cylinder andhaving one end connected to one of the metallic cylinders, acontact-maker resting on the coil and so connected to the other metalliccylinder that it always occupies the same position relatively to it, anda metallic bar interposed in the circuit between the two metalliccylinders.

6. The combination of two concentric metallic cylinders, anon-conducting cylinder fixed inside and projecting beyond the outermetallic cylinder, such cylinder being free to move outside the innermetallic cylinder, a

coil wound on the projecting portion of the non-conducting cylinder andhaving one end connected to the outer metallic cylinder, a metallic barconnected to the inner metallic cylinder and a contact-maker fixed tothe bar and resting on the coil.

7 The combination of two concentric metallic cylinders, a non-conductingcylinder fixed to and projecting beyond one of them such cylinder beingadapted to fit between the two metallic cylinders, a coil Wound on theprojecting portion of the non-conducting cylinder and having one endconnected to one of the metallic cylinders, a contact-maker resting onthe coil and so connected to the other metallic cylinder that it alwaysoccupies the same position relatively to it, and a glow Vessel carriedby the outer metallic cylinder.

8. The combination of two concentric metallic cylinders, anon-conducting cylinder fixed to and projecting beyond one of them suchcylinder being adapted to fit between the two metallic cylinders, a coilWound on the projecting portion of the non-conducting cylinder andhaving one end connected to one of the metallic cylinders, acontact-maker rest ing on the coil and so connected to the othermetallic cylinder that it always occupies the same position relativelyto it, a metallic bar interposed in the circuit between the two metalliccylinders, and a glow vessel carried by the outer metallic cylinder.

9. The combination of two concentric metallic cylinders, anon-conducting cylinder fixed inside and projecting beyond the outermetallic cylinder, such cylinder being free to move outside the innermetallic cylinder, a coil wound on the projecting portion of thenon-conducting cylinder and having one end connected to the outermetallic cylinder, a metallic bar connected to the inner metalliccylinder, a contact-maker fixed to the bar and resting on the coil, anda glow vessel carried by the outer metallic cylinder.

10. An apparatus for measuring the lengths of electric waves, comprisinga closed circuit containing inductance and capacity, the elements of thecircuit being so constructed and arranged that the movement of a singlepart will simultaneously vary the inductance and capacity of thecircuit.

11. An apparatus for measuring the lengths of electric waves, comprisinga closed circuit containing inductance and capacity, the elements of thecircuit being so constructed and arranged that the movement of a singlepart will simultaneously vary the inductance and capacity of thecircuit, a pointer connected to the movable part, and a scale with whichthe pointer cooperates.

JOHN AMBROSE FLEMING.

Witnesses:

H. D. JAMEsoN, T. L. RAND.

